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Sierra Ladrones Formation
Geologic formation in New Mexico, United States From Wikipedia, the free encyclopedia
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The Sierra Ladrones Formation is a geologic formation exposed near the Rio Grande Valley in New Mexico. It preserves fossils of Pliocene to Pleistocene age.[1]
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Description
The formation consists of three facies representing different depositional environments. These are piedmont slope and alluvial fan deposits, typically composed of light-brown to light-reddish-brown sandstone and fanglomerate; axial stream deposits, which are composed of light-gray to light-yellowish-brown fine- to medium-grained sand and sandstone with fluvial cross-bedding and cut-and-fill channels; and interbedded basalt flows with a K-Ar age of 4.5 +/-0.1 million years (Ma. The total thickness is in excess of 470 m (1,540 ft).[1] The formation unconformably overlies or is in fault contact with the Popotosa Formation or older formations. Its age is early Pliocene to middle Pleistocene (2 Ma to 5 Ma.)[1]
The formation is interpreted as fanglomerates shed from the flanking uplifts of the Rio Grande Rift and channel and floodplain deposits of the ancestral Rio Grande.[2]
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Fossils
The formation has yielded abundant fossils of Irvingtonian age at Tijeras Arroyo, south of Albuquerque International Airport. These include Hypolagus, Equus, Mammuthus, and Hesperotestudo.[3]
History of investigation
The formation was defined by M.N. Machette in 1978 for exposures in the Sierra Ladrones, a range of low foothills of the Ladron Mountains, in the Sevilleta National Wildlife Refuge.[1]
The formation was subsequently mapped into the lower Rio Puerco valley[4] and as far north as the Santo Domingo basin.[5]
Footnotes
See also
References
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